The present application relates to a prosthesis for femur replacement surgery and more particularly to a prosthesis which receives a modular neck assembly selected for a desired neck length, neck angle, anteversion and offset.
Surgery to replace the femur in total joint surgery involves the insertion of a stem in a cavity formed in the femur. The end of the stem extending from the cavity has a neck which is formed at an angle and the neck is mated with a socket in the hip. Every patient requires individual fitting due to the unique anatomical requirements of the particular patient. A prosthesis in which the stem and neck are a unitary device requires that the surgeon have a large quantity of prostheses available to provide a correct bio-mechanical function of the prosthesis with the patient. It is very costly to maintain a large inventory of prostheses and, despite the number of prostheses available, quite often the appropriate size and angle are not completely met.
More recently, modular prostheses have been designed to overcome this longstanding problem. The modular designs have each focused on a different aspect of the prosthesis. U.S. Pat. No. 4,919,670 to Dole et al disclose a tapered cylindrical lock mechanism disposed on the proximal end surface of the stem and the head mechanism including a complementary tapered aperture for receiving the cylindrical lock mechanism in a rigid mechanical coupling engagement. In U.S. Pat. No. 4,995,883, Demane et al disclose a modular hip prosthesis which can be custom fitted to a patient before surgery. A plurality of prostheses bodies, pads, heads, collars and extension sleeves are offered in various sizes. An elongated bolt extends through the prosthesis body and is connected to the extension sleeve. Luman, in U.S. Pat. No. 5,002,578 discloses a modular hip stem prosthesis apparatus which includes a hip stem with an integral, enlarged shoulder and a neck section mountable to the hip stem which are releasably interconnected with a bolt. The annular relation between the side arm and the longitudinal axis of the hip stem is selectively predetermined. In U.S. Pat. No. 5,002,581, Paxson et al disclose a modular hip joint prosthesis with adjustable angular variation. This variation is made possible by having the axis of the connection part of the stem and neck being angularly offset from the axis of the body of the stem and neck, respectively. Pappas et al, in U.S. Pat. No. 5,030,234 disclose a modular stem prosthesis which has a stem connected to an extension with a slip fit interconnection. Engagement between the stem and the extension is provided by deflectable end portions of one component of the prosthesis which are engaged in a mating deformation with the other component. Fallin, U.S. Pat. No. 5,108,452, is a continuation-in-part of Demane et al and discloses removable pads attached to the prosthesis body with a wedge to lock the connection between the prosthesis and the hip joint. In U.S. Pat. No. 5,286,260, Bolesky et al disclose a modular hip prosthesis for replacement of a portion of the femur comprising a kit that includes an upper and lower portion. A neck member is also provided to rigidly attach the head member to the body member. McTighe et al in U.S. Pat. No. 5,653,765 disclose a modular hip stem prosthesis having a neck member extending angularly outward from the shoulder piece and configured to receive a spherical hip ball for insertion into the hip socket. A locking screw securely joins the shoulder piece with the stem.
A further complication in the total joint surgery to replace the femur is that clinically, the metal of the prosthesis is not compatible with the bone on a modular scale. The different moduli of the bone and the metal causes a stress path to pass through the more rigid material and the stress between the bone and metal occurs distally shielding the proximal femur from stress. This results in atrophy of the proximal femur and pain to the patient and eventually, possible failure. To alleviate this problem, Averill et al in U.S. Pat. No. 4,888,023, disclosed a prosthesis with a fixation resistant finish on the external peripheral surface of the distal tip. The distal tip is selectively removable and replaceable. In U.S. Pat. No. 4,892,546, Kotz et al disclose an adjustable prosthesis for a joint bone having an elongated inner sleeve and an outer sleeve. The inner sleeve is telescopically slidable within the outer sleeve but is not rotatable. The inner sleeve includes a threaded spindle nut and a threaded spindle which are positioned within the inner sleeve. In U.S. Pat. No. 5,057,101, Dorr et al disclose a femoral prosthesis with a centering sleeve wherein the sleeve is removably attached midway along a stem of the prosthesis. Removable sleeves are disclosed.
Montagne in European Patent No. 0 201 407 A1 discloses a prosthesis with connecting members which are adjustable with an octagonal fitting. A sleeve is not disclosed on the shank of the prosthesis. Frey in European Patent No. 0 187 903 A1 discloses an adjustable hip joint prosthesis with an outer sleeve having an inner polyethylene liner. The outer sleeve has an outer surface with self-tapping threads to be screwed to the femur. In WIPO publication WO 94/07438, Tronzo discloses a bearing mechanism built into a femoral component which has a sleeve. The sleeve is disposed at the distal portion of the stem and buttresses a bearing retaining shoulder. Walker in WIPO publication WO 91/03992 discloses a prosthesis with a plastic sleeve having a non-uniform bore.
Despite the recognition and activity directed to solving these longstanding problems, none of the above-identified patents have been widely accepted and prostheses based on these references have not made a significant impact in the field. The problem still exists.
It is an object of the present invention to provide a prosthesis for use in femur replacement surgery which has a modular neck assembly which is selected to provide a predetermined neck length, neck angle and anteversion to meet the unique anatomical requirements of the individual patient and provide the correct force line to transfer the stresses into the anatomical plane of the femur.
It is a further object of the present invention to provide a sleeve on the prosthesis for distal micro motion to avoid stress shielding proximally.
It is yet another object of the present invention to permit the surgeon to provide a prosthesis adapted for the individual patient while maintaining a minimum number of prostheses in stock.
It is still another object of the present invention to provide a prosthesis having a porous coating to facilitate biological in-growth.
In accordance with the teachings of the present invention, there is disclosed a prosthesis for femur replacement surgery having a stem having a vertical axis which is adapted to be received in the femur. The stem has a bore formed therein, the bore being at an angle with respect to the vertical axis of the stem. A modular neck assembly has a first end portion having a length and a second end portion. A socket is formed on the second end portion of the modular neck assembly. Means are provided for receiving a desired length of the first end portion of the modular neck assembly in the bore in an upper portion of the stem and retaining the modular neck assembly therein at a desired neck angle and at a desired degree of rotation therebetween to provide a desired degree of anteversion. In this manner, surgeon may select a desired neck length, neck angle, anteversion and offset for a particular patient undergoing surgery. The prosthesis has an outer surface contacting the femur, the outer surface having thereon a porous coating facilitating biological in-growth with the femur.
In further accordance with the teachings of the present invention, there is disclosed a prosthesis for femur replacement surgery having a stem having a vertical axis which is adapted to be received in a canal formed in the femur. The stem has an upper portion and a lower portion. The lower portion has a uniform diameter and tapers to a point. A unitary sleeve made substantially of metal has a uniform inner diameter slightly greater than the uniform diameter of the lower portion of the stem. The lower portion of the stem is received in the sleeve which is adapted to be press-fitted within the canal in the femur. The lower portion of the stem is circumferentially movable with respect to the sleeve and the stem has micro-motion along the vertical axis of the stem with respect to the sleeve.
In yet another aspect, there is disclosed a prosthesis for femur replacement surgery. A stem has a vertical axis which is adapted to be received in a canal formed in the femur. The stem has an upper portion and a lower portion, the upper portion having an outer surface. A porous coating is formed on the outer surface, the porous coating facilitating biological in-growth with the femur.
In still another aspect, there is disclosed a prosthesis for femur replacement surgery having a stem having a vertical axis which is adapted to be received in a canal formed in the femur. The stem has an upper portion and an opposite lower portion. The upper portion has a blind bore formed therein, the bore being at an angle between 100xc2x0 and 140xc2x0 with respect to the vertical axis of the stem. The lower portion is of uniform diameter and tapers to a point. A modular neck assembly has a first end portion and an opposite second end portion, the first end portion being formed at a desired angle with respect to the second end portion. The first end portion of the modular neck assembly is received in the blind bore in the stem such that the second end portion of the modular neck assembly is at a desired angle with respect to the vertical axis of the stem. A first keying means is formed in the blind bore in the stem and a cooperating second keying means is formed on the first end portion of the modular neck assembly such that the modular neck assembly may be rotated to a desired degree of anteversion and inserted into the bore such that the first and second keying means cooperate and rotation of the modular neck assembly within the bore is prevented. A unitary sleeve made substantially of metal has a uniform inner diameter slightly greater than the uniform diameter of the lower portion of the stem. The sleeve is adapted to be press-fitted into the canal in the femur. The lower portion of the stem is received in the unitary sleeve, there being circumferential movement of the lower portion of the stem with respect to the sleeve and the sleeve having micro-motion between the upper portion and the lower portion of the stem.
A method of using the prosthesis is disclosed.
These and other objects of the present invention will become apparent from a reading of the following specification taken in conjunction with the enclosed drawings.